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Abstract

We present the first analysis of the jitter sensitivity of a superconductive digital-to-analog converter (DAC)for use as a reference RF source. This analysis is important for maintaining quantum-accurate voltage output as we extend our superconductor-based DAC systems to gigahertz frequencies. We study single frequency tones from 100 kHz to 1 GHz,synthesized from delta-sigma encoded digital bitstreams. We quantify the impact of random and deterministic jitter on (1)the output amplitude of the fundamental tone and (2) the inband Signal to Noise and Distortion Ratio (SNDR) and Spurious Free Dynamic Range (SFDR). The advantages in jitter sensitivity and noise performance of the pulsed-output system relative to a semiconducting zero-order-hold DAC are also quantified. Using this analysis, we determine performance limits on the capability of our system as a function of output frequency and DC bias current. We show that random jitter up to 1 ps RMS will have negligible impact on the accuracy and noise floor for synthesized tones up to 1 GHz. Deterministic timing jitter of up to 5 ps due to DC bias current is shown to decrease the single-tone output amplitude by up to 600 V V at 1 GHz. Such jitter will also degrade the in-band SNDR to 12 dB at 1 GHz, compared to the baseline delta-sigma encoding digitization noise floor of 70 dB. Finally, harmonic generation due to deterministic jitter will degrade the in-band SFDR for synthesis of single tones below 5 MHz. Experimental results that verify the expected harmonic generation due to deterministic jitter are shown for single tones generated at frequencies 100 kHz to 3 MHz.

Citation: IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control